1. Field of Invention
This invention relates generally to the conversion of tire deflection mechanical energy from tires to electrical energy.
2. Description of Prior Art
Generating electrical energy using electroactive polymer (EAP) generators is disclosed in U.S. Pat. Nos. 7,049,732, 7,034,432, 6,940,211 and 6,812,624. Thermal energy to electrical energy conversion using EAP generators is disclosed in U.S. Pat. No. 6,628,040. Use of EAP transducers for conversion of deflection mechanical energy, in backpacks, to electrical energy is disclosed in U.S. Pat. No. 6,982,497. A means for converting biologically generated mechanical energy into electrical energy is disclosed in U.S. Pat. No. 6,768,246. In this application, EAP transducers are positioned in the heels of footwear so that deflections are imparted to the transducers. The deflections result from forces imparted the footwear heels from the heels striking the walking surface.
An additional application for EAP generators is for recovery of deflection mechanical energy from wheels used for transportation. A wheel transports a load by rolling over a surface. Typically, wheels used for transportation are comprised of a structural rim and an air inflated tire. The structural rim is affixed to a transport vehicle and provides the load path between the transport vehicle and air inflated tire. The air inflated tire contacts and conforms to the surface. The tire conforms to the surface by deflecting to match the contour of the surface.
EAP generators are uniquely suited for harvesting electrical energy from tire deflection mechanical energy. That is because EAP transducers can accommodate relatively large deflections with a large range in deflection frequencies. For example, EAP materials can sustain strains greater than 200%. This allows for mechanical energy recovery from relatively large deflections. Deflection frequencies can range from greater than zero to hundreds of Hz.
In many applications, a series of numerous EAP generators are assembled to produce usable quantities of electrical energy. EAP generators are relatively inexpensive, lightweight and are comprised of few moving parts. This makes their use cost effective.
There are examples of small strain materials that are been used to convert mechanical energy to electrical energy. These materials include piezoelectric ceramics such as lead zirconium titanate. The strain levels for these types of materials are limited to approximately 1.5%. Densities of these materials typically are above what is practical for use in mobile applications. A similar material to piezoelectric materials is EAP material “irradiated polyvinyidene” (PVDF). This material is suitable for use up to approximately 4% strain. However, this level of strain is also not suitable for the relatively large tire deflections.
Conventional electromagnetic generators are not suitable for tire deflection application because of their mechanical complexity and are relatively heavy. A typical electromechanical generator includes multiple coils of electrical wire with multiple moving parts. Typically the materials used to manufacture conventional electromechanical generators have high density relative to that of EAP generator materials. The materials and complexity of conventional electromechanical generators make them less cost effective than EAP generators. In addition, the weight of electromechanical generators makes them less suited than EAP generators for mobile electrical energy recovery.
When a loaded wheel contacts a road surface, the tire conforms to the road surface by deflecting. The unloaded portion of the tire remains circular. The loaded portion of the tire typically sustains radial deflections of approximately between 0.5 and 0.75 inches. In typical applications, wheels can transport loads that range from a few hundred pounds to a few thousand pounds. Energy is required to deflect the inflated tires. The magnitude of energy, for each tire, is the force on each tire multiplied by the radial deflection. EAP generators can be assembled in a load transporting wheel in a configuration to recover a portion of this mechanical deflection energy.
Automobiles are required to start, accelerate, operate at steady state, decelerate, and stop. The energy to accelerate and maintain the velocity of the automobile is provided through the chemical combustion in an internal combustion engine. Breaks are used to decelerate an automobile. Deceleration results in a loss of kinetic energy. Breaks dissipate this kinetic energy by friction. Friction converts the kinetic energy into heat energy.
An example of mechanical energy to electrical energy conversion is demonstrated by hybrid automobiles. Deceleration requires the automobile to dissipate kinetic energy. Hybrid automobiles employ technology that reconverts a portion of this dissipated kinetic energy. This is accomplished by converting the breaking force into torque. This torque is then used to generate electricity with conventional electromagnetic generators. The electricity is then stored and used at a later time. The stored electric energy is used to operate electric motors. These motors are used in conjunction with internal combustion engines for propulsion. This reduces the internal combustion engine fuel consumption and increases the overall operational efficiency of the automobile.
Use of hybrid automobiles can result in significant gains in fuel use efficiency for urban operation. A significant portion of automobile operation time, in an urban environment, is devoted to acceleration and deceleration. As a result, a significant portion of vehicle operational energy can be recovered from vehicle deceleration.
For conditions where a large portion of the operational time is steady state operation, the available energy for conversion from deceleration is minimal. As a result, the gains in operational efficiencies provided by hybrid automobiles are reduced significantly.
EAP generators could be used in hybrid automobiles for electrical power generation during acceleration and steady state operation. Electrical energy can then be recovered any time the automobile travels from one point to another. This provides a means for taking advantage of hybrid automobile operational efficiencies in all operational environments.
In addition, EAP generators could also be used in all-electric automobiles. The General Motors EV1 all-electric automobile is a demonstration of current all-electric technology. All-electric automobiles are powered by battery stored electrical energy. Battery storage capability technology limits the mileage range per charge of these types of automobiles. The advantage the EAP generators would provide is to increase the vehicle's range per charge.
EAP generators could also be used in stationary applications. For example, conveyor belts are used to transport loads from one location to another. Typically, conveyor belts are comprised of a flexible belt that is supported by a series of wheels. These wheels could be configured with EAP generators. The rotation of the support wheels could then recover the wheel deflection energy. This recovered energy could then be used to provide a portion of the power to operate the conveyor belt, thereby reducing overall power consumption of the conveyor belt.